k8s needs a control plane, that needs security, hence all the tokens, certs (which need internal and external IPs and FQDNs), also it needs to set up an overlay network (so you need to configure the CNI provider, sysctl stuff for ebtables and iptables/nftables to work correctly), and DNS, and a dashboard would be nice too. oh, and unless you use k3s or something that budles a container runtime (CRI provider) you need to setup one (eg docker).

it's understandably complex, even if many parts are pretty standard (eg. the sysctl stuff, and installing dependencies is basically dnf/yum/apt/apk or exit and let the user do it).

since the most error prone parts were/are setting up the TLS stuff that got automated first (in the form of kubeadm install), and the rest just remains in "run this" form.

but the k3s installer is just a one liner call to a bash script. though then you have to make sure to include the magic env vars to get what you want.